-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 This nice NSDI 09 paper has an interesting related discussion
http://www.usenix.org/events/nsdi09/tech/full_papers/nychis/nychis.pdf Still, I'm afraid you can't avoid putting some processing on the FPGA. Ruben On 1/27/10 12:35 , Harald Schioeberg wrote: > > > Juan Ramon Gutierrez Agullo wrote: >> Hello everyone > >> This is my first message here and, of course, I'm a newbie click user. > >> I have an 802.11a transmitter >> (https://www.cgran.org/wiki/ftw80211ofdmtx) running in the USRP2, but it >> only generates a standard-compliant IEEE802.11a/g/p OFDM frame - PHY >> layer. >> Looking at other projects I found the hydra project, and they used click >> to implement the MAC layer (CSMA/CA and DCF). I have some questions and >> I hope you could help me. > > USRP uses either usb (USRP1) or ethernet(USRP2) to communicate with the > host, which probably means delays in the magnitude of 10s of us for a > frame-transmission over the interface (Take Linux' interrupt latency for > ethernet-frame-reception into account!) > > 802.11 slot time is 4 us, which is the time you have available to > > a) receive the last sample at the frontend > b) decode it at the CPU > c) deceide whether to ack it > d) encode the ack at the CPU > e) have the first samples available for transmission at frontend > > Click runs on the host as a scheduled kernel process, which brings you > to probably 100s of us worst case reaction on incoming samples, > especially on a Linux machine busy decoding samples. > > So I don't see any way to implement 802.11 MAC on USRP on the host side, > no matter whether you use click or any other host side tool, IMHO: the > FPGA is your only choice (maybe some fancy real-time kernels might just > make it...) > > Please, please, prove me wrong on that, 802.11 on USRPs would be soooooo > cool. > >> - How can click communicate with GNU Radio? > > My approach would be: > a) implement the MAC on the FPGA, > b) implement TX-queues on the FPGA that use this MAC, > c) write a driver that accepts frames and meta-data for this MAC, > d) write a click element, that takes Ethernet packets and transforms it > into one of these meta-annotated-frames. > e) implement things like rate control or scheduling algorithms as click > elements and have them set proper packet meta-data. > >> - Is there any MAC implementation -by default- with click installation? > > Nope, as all Wifi cards implement the MAC in hardware, for above > mentioned reasons. > > Now, can sombody please tell this poor guy that I'm a moron and there is > a smooth and simple way to do all this .... > > Harald _______________________________________________ click mailing list [email protected] https://amsterdam.lcs.mit.edu/mailman/listinfo/click - -- Ruben Merz Deutsche Telekom Laboratories http://www.net.t-labs.tu-berlin.de/people/ruben_merz.shtml -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iQEcBAEBAgAGBQJLYEQDAAoJEIem9YkUyRjt+YEH+wRP2+mDh+Ls9bbegWksj+lC sI2Slql/GYE8rHQiIPu9/XhyrkSfDNsJdpiN09vcjsEI3T8U6Ee3X1eTeUeSoNOd jVQxXTDuxMYIkuR2sx8vK1FUzPJJkc79TfLdXJKi4o3Fyv197d+t4zEd1a4TxbhV 7zFzUyELhbo7sk+BWfVm1oj3jVQApO28aJwiaWKr5uCeOIZjxZqR8RDcpYJCw2V1 /A06s6geBb3a74B6gK192D7tLSERON8FPrfSY8DRpR66PRHeVMVJneAY3RU9I3cr rTpPxGw2BZKJNKeicHv4r7L3HY2heSESNzxt+uM3OZSfBzQLiPw26rKxdWQK8Ak= =IeD4 -----END PGP SIGNATURE----- _______________________________________________ click mailing list [email protected] https://amsterdam.lcs.mit.edu/mailman/listinfo/click
